Consult an ophthalmologist (eye surgeon) for detailed retina evaluation, and show your anti tb medicines. If the problem is due to any of these medicines, it can be usually reversed on stopping the same.

Get treatment for allergy from child specialist doctor and after that, get the eyes checked up by an ophthalmologist or eye surgeon. It will clear with simple medicines.
You can also opt for online consultation for the eye problem.

Squint is not a reason for rejection in medical test. It depends on for what purpose you are going. Your visa agent or job consultant can guide you. If in doubt, consult an ophthalmologist (eye surgeon) again.

Simple reasons could be infection or allergy (conjunctivitis), or there could be more complicated reasons. Difficult to tell only by query. It is better to consult an ophthalmologist in clinic or upload some photos for an online consultation.

Watering from eyes during yawning is quite common. It is a normal variation and does not need any treatment. Wash your eyes with fresh, cool water. That is enough. Since you have cylindrical power in left eye, it can cause headache if you are not wearing glasses full time. If your eye check up by an ophthalmologist is recent, observe for few more days for the headache to improve. Or, you may have to recheck if your existing glass power is ok or changed.